Perfluoroalkyl surfactants are commonly used in the preparation of aqueous fire-fighting foams (AFFFs). These surfactants are effective when used in preparing foams used to extinguish fires caused by non-polar fuels such as hydrocarbons, and act by covering the surface of the burning fuel with a vapor-suppressing film. However, such foams are ineffective in fighting fires caused by polar solvents, such as alcohols, ketones, or tetrahydrofuran, because the foam is destroyed by mixing with the water-miscible fuel.
To address this problem, so-called alcohol-resistant firefighting foams (AR-AFFFs) have been developed. AR-AFFF formulations contain water-soluble polymers that prevent the foam from collapsing on polar fuels and that also significantly lengthen the foam drain time by increasing the viscosity of the aqueous phase. The polymers most commonly used are polysaccharides such as xanthan and rhamsan gums. The dissolved gum precipitates from the foam solution when it contacts the polar fuel and forms a soft mat, or membrane, between the foam blanket and fuel to block further intermixing. However, the high concentrations of polysaccharide gums necessary to make an effective AR-AFFF concentrate can cause the concentrate to be so thick that the concentrate is difficult to pump efficiently, and therefore can cause proportioning problems during foam generation and application. The use of certain fluoropolymer surfactants has the same polar fuel performance as xanthan gums, but with much lower viscosity increase. See, for example, U.S. Pat. No. 6,156,222. Therefore, a significant portion of the gum can be replaced by fluoropolymer surfactants to give better AR-AFFF performance.